A server and a user's PC are points of origin and termination of data, and such an origin or termination point is referred to as an end system (ES).
A network connects ESs together, and a device present between ESs is referred to as an Intermediate System (IS). The ISs guide data to a destination to enable communication between ESs. Some examples of the ISs are a switch, a router, etc.
A proxy server refers to a computer or application program that allows a client to indirectly connect to a server on another network that provides services through the proxy server itself. The proxy server functions as a relay between a server and a client. A function of performing communication on behalf of the server or the client is referred to as a ‘proxy’, and a device that performs such a relay function is referred to as a ‘proxy server’.
In a system using a proxy server, the proxy server functionally serves as ISs but actually as an ES. Communication between a user's PC and a proxy and communication between the proxy and a server are performed over separate networks, and the proxy only relays data. A source IP address in a packet header being delivered during communication is used as an IP address of the user's PC in the communication between the user's PC and the proxy and as an IP address of the proxy in the communication between the proxy and the server. Thus, the server suffers from the inconvenience of not being able to process a packet before providing a service using the source IP address in the packet.